Increased use of radio and microwave frequencies requires investigations of
their effects on living organisms. Duckweed (Lemna minor L.) has been
commonly used as a model plant for environmental monitoring.

In the present
study, duckweed growth and peroxidase activity was evaluated after exposure
in a Gigahertz Transversal Electromagnetic (GTEM) cell to electric fields of
frequencies 400, 900, and 1900 MHz.

The growth of plants exposed for 2 h to
the 23 V/m electric field of 900 MHz significantly decreased in comparison
with the control, while an electric field of the same strength but at 400
MHz did not have such effect. A modulated field at 900 MHz strongly
inhibited the growth, while at 400 MHz modulation did not influence the
growth significantly. At both frequencies a longer exposure mostly decreased
the growth and the highest electric field (390 V/m) strongly inhibited the
growth. Exposure of plants to lower field strength (10 V/m) for 14 h caused
significant decrease at 400 and 1900 MHz while 900 MHz did not influence the
growth.

Peroxidase activity in exposed plants varied, depending on the
exposure characteristics. Observed changes were mostly small, except in
plants exposed for 2 h to 41 V/m at 900 MHz where a significant increase
(41%) was found.

Our results suggest that investigated electromagnetic
fields (EMFs) might influence plant growth and, to some extent, peroxidase
activity. However, the effects of EMFs strongly depended on the
characteristics of the field exposure.